Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-09-11
2002-05-21
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06392967
ABSTRACT:
FIELD OF INVENTION
The present invention is directed to a method and device for measuring characteristics of an optical pickup or optical disc. The present invention incorporates a recording and/or reproducing system of optical disc.
BACKGROUND
It is currently known that there has been an inspection device for characteristic of optical pickup, which has been used for optical disc drive. The inspection device for characteristic of optical pickup, for example, is used for shipping inspection (inspection of optical pickup before shipping) or accepting inspection (inspection of optical pickup prior to accepting) of optical pickup, etc. It inspects whether optical pickup satisfies prescribed specifications.
FIG. 3
shows a block configuration of a known inspection device for characteristic of optical pickup. The inspection device for characteristic of optical pickup
100
, shown in the
FIG. 3
, includes the following: optical pickup
101
, which will be an inspection object; test bench
102
, where optical disc will be set; matrix circuit
103
, to which the output from a photo detector possessed by optical pickup
101
, will be provided, and which will output reforming (RF) signals; and servo control circuit
104
, which will servo control for the reproducing drive of optical disc, based on the output from the matrix circuit
103
.
In addition, the inspection device for characteristic of optical pickup
100
, also has the following: measuring circuits
105
a
-
105
n
, each of which will measure the various values of characteristics of optical pickup, based on the output from the matrix circuit
103
; multiplexer
106
, which will switch the output from the measuring circuits
105
a
-
105
n
; analog/digital converting circuit
107
, which will convert the output from one of the circuits, which has been converted by internal multiplexer
106
of each measuring circuit
105
a
-
105
n
, into digital data; and computer
108
, which will perform statistical application on the output data from the analog/digital converting circuit
107
, and will display the results.
Optical pickup
101
is an inspection object for the inspection device for characteristic of optical pickup
100
. This optical pickup
101
can, for example, be installed to the inspection device for characteristic of optical pickup
100
, and be freely attached or removed.
The optical pickup
101
also has laser diode, beam splitter, object lens, and photo detector, etc. Furthermore, the optical pickup
101
lets laser emitted from laser diode gather on the optical disc through beam splitter, object lens, etc. Then, the optical pickup
101
lets reflected light from an image on photo detector. The photo detector possessed by the optical pickup
101
, is photoelectric conversion element; it converts the reflected light which has formed an image, into electric signals.
In general, the optical pickup
101
has multiple photo detectors: for example, it has a photo detector divided into a quarter in cross-shape; and it also has another photo detector for detecting side spot at both sides of the above photo detector divided into a quarter in cross-shape. The output from such photo detectors will be provided to the matrix circuit
103
.
The test bench
102
, where optical disc will be set, rotates and drives the optical disc in order to reform the optical disc. In addition, the optical disc which will be set in the test bench
102
, is used as a reference for the inspection device for characteristic of optical pickup
100
.
The matrix circuit
103
, to which the output from each photo detector possessed by the said optical pickup
101
will be provided, generates reforming (RF) signals, focus error (FE) signals, and tracking error (TE) signals, etc. from the output from such photo detectors.
For example, if photo detectors possessed by the optical pickup
101
consist of the one divided into a quarter in cross-shape and the one used for side spot, the matrix circuit
103
will detect each signal as follows: the matrix circuit
103
processes the total sum of each output, based on the output from the photo detector divided into a quarter, then outputs the result of processing as RF signals. The matrix circuit
103
processes the sums of the output from two (2) photo detectors which are an object at the center of a cross-shape, and processes the difference between these sums, then outputs the result of processing as FE signals. Therefore, the matrix circuit
103
outputs FE signals, by using the astigmatism or astigmatic method. In addition, the matrix circuit
103
processes the difference between the outputs, based on the output from the photo detector used for side spot, then outputs the result of processing as TE signals.
The matrix circuit
103
provides RF signals, FE signals, and TE signals, which are processed as the above mentioned, to servo control circuit
104
and measuring circuits
105
a
-
105
n.
The servo control circuit
104
servo-controls as reproducing drive of optical disc, based on the RF signals, FE signals, and TE signals. More specifically, the servo control circuit
104
performs focus servo control, tracking servo control, thread servo control, and tilt servo control.
The measuring circuits
105
a
-
105
n
operate the characteristics value of the optical pickup
110
. Each measuring circuits
105
a
-
105
n
measures different characteristics values. Therefore, the inspection device for characteristic of optical pickup
100
is equipped with the number of measuring circuits
105
a
-
105
n
, which are equivalent to the number of the characteristics values to be measured.
Furthermore, each measuring circuits
105
a
-
105
n
performs filtering processing by analog processing, peak detecting processing, and frequency/voltage conversion processing, and measures characteristics values. The first measuring circuits
105
a
, for example, measures the level of signals with “S” shaped curve during leading-in of a focus servo loop, based on FE signals. The second measuring circuits
105
b
, for example, measures the level of TE signal, based on the TE signals. The third measuring circuits
105
c
, for example, measures the level of RF signal, based on the RF signals. Finally, the forth measuring circuits
105
d
, for example, measures the jitter component of RF signal, based on the RF signals.
Multiplexer
106
switches the output from each measuring circuits
105
a
-
105
n
, then supplies the output from either of the measuring circuits to the analog/digital converting circuit
107
.
The analog/digital converting circuit
107
converts the output from each measuring circuit
105
a
-
105
n
, which has been provided through the multiplexer
106
, into digital data, then supplies it to the computer
108
. The conversion speed of the analog/digital converting circuit
107
is slow, because the output from each measuring circuit
105
a
-
105
n
is almost at DC level. For example, the conversion speed of the analog/digital converting circuit
107
is about 1 KHz.
The computer
108
performs statistical application on digital data supplied from the analog/digital converting circuit
107
, then displays the results.
As we have discussed in the above sections, the current inspection device for characteristic of optical pickup
100
measures the characteristics value of the optical pickup
101
, by using the measuring circuits
105
a
-
105
n
which are equipped to be the same number of the characteristics values to be measured, then displays the results to users, by using the computer
108
.
However, the current inspection device for characteristic of optical pickup
100
has measured the characteristics value of the optical pickup
101
, by using the multiple measuring circuits
105
a
-
105
n
through analog processing. Therefore, the current inspection device for characteristic of optical pickup
100
has had a problem that stable characteristics value cannot be obtained, because some effect is generated by uneven characteristics or elapsed change of each measuring circuit
105
a
-
105
n
. Furthermore, there has been anot
Hashimoto Yukari
Kohama Shunsuke
Nakayama Akihito
Shintani Kenji
Frommer William S.
Frommer & Lawrence & Haug LLP
Sony Precision Engineering Center (S) Pte. Ltd.
Tran Thang V.
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